Amplitude of Somatosensory Evoked Potentials (SEPs) in Short-Latency SEPs Condition is 80% of that in Giant SEPs

The recording conditions of somatosensory evoked potentials (giant SEPs) are different from those of short-latency SEPs (SSEPs). We investigated the waveform characteristics obtained for each condition. Forty-eight upper limbs of 24 adult normal subjects (12 males, age 35.5 ± 9.7 years (mean ± SD)) were investigated. The main differences in recording conditions were reference electrodes (giant SEPs: the earlobe electrode ipsilateral to the stimulated limb, SSEPs: Fz), stimulus rate (1 Hz, 5 Hz), and bandpass filter (1 Hz–1 kHz, 20 Hz–3 kHz). SEPs were elicited by unilateral percutaneous electrical stimulation of the median nerve at the wrist. The amplitudes of N20o–N20 and N20–P25 were significantly larger in the giant SEP condition than in the SSEP condition (p<0.001). The mean + 3SD of N20–P25 amplitude was 10.0 µV in the giant SEP condition and 7.8 µV in the SSEP condition. The N20–P25 amplitude was significantly correlated between the giant SEP and SSEP conditions (R=0.64, p<0.001). Thus, the amplitude of SEPs in the SSEPs condition is equivalent to 80% of that in the giant SEPs condition. The information is useful for detecting cortical hyperexcitability in various neurological disorders including myoclonic epilepsy.